Smokeless powder



Unite States Patent 2,865,728 Patented Dec. 23, 1958 Free SMOKELESS POWDER Ralph L. Cook, Alton, Ill., assignor to Olin Mathieson Chemical Corporation, East Alton, [1]., a corporation of Virginia No Drawing. Application May 17, 1955 Serial No. 509,120

7 Claims. (Cl. 52-5) This invention relates generally to smokeless powders and more particularly to progressive burning smokeless powders having a coating of new and improved deterrent materials.

Smokeless powder grains are surface treated with deterrents in order to obtain maximum projectile velocities with minimum breech pressures in the firearm. The deterrent coating decreases the combustion rate of the initially burning portion of the powder grain. Many materials have been proposed for use as deterrents in smokeless powder such as, for example, dinitrotoluene, the normal dialkylphthalates, dialkyldiarylureas, and many waxes, fats and synthetic resinous materials. Although each of these heretofore proposed deterrents is effective on freshly prepared smokeless powder grains it migrates into the grains in storage and loses its effectiveness. This is particularly true if the powder grains contain a liquid explosive nitric ester such as nitroglycerin or if the grains are stored at elevated temperatures for any extended period of time.

It is, therefore, an object of this invention to provide smokeless powder grains having a coating of deterrent material devoid of the foregoing disadvantages. Another object of this invention is to provide smokeless powder grains and particularly double base smokeless powder grains having improved ballistic characteristics after extended periods of storage under adverse temperature conditions.

In accordance with this invention, generally speaking, the foregoing objects as well as others are accomplished by providing smokeless powder grains having a surface coating of a diisoalkylphthalate. The diisoalkylphthalate should have from 3 to 6 carbon atoms in the alkyl chain in order to be adapted for properly treating the surface of the grains and for obtaining optimum ballistic characteristics. Diisopropylphthalate, diisobutylphthalate, diisoamylphthalate, and diisohexylphthalate fall within this group of phthalates. For best results, at least about 2% of the diisoalkylphthalate should be utilized and ordinarily not more than about 15% will be required. The deterrents of this class have been found well suited for use with nitrocellulose base or other single base powder grains and are especially well suited for use in double base smokeless powder grains containing a liquid explosive nitric ester in combination with nitrocellulose, nitrostarch or the like.

The deterrents of this class may be applied to the grain by any process which will satisfactorily distribute the material over the surface of the grain and achieve proper penetration of the outer envelope thereof. For

best results, the deterrent should be located in the outer one-sixth of the web of the grain after it has been treated. The process disclosed in the McBride U. S. Patent 1,955,927 has been found particularly advantageous for properly locating the deterrent on the smokeless powder grain. Smokeless powder grains formed by conventional extrusion methods or by one of the globular powder processes such as that disclosed in the Schaefer patent U. S. 2,160,626 or by any other process and having a coating of one of the diisoalkylphthalates, or mixtures thereof, come within the purview of this invention. The liquid explosive nitric ester may be applied to the surface of the grains by any suitable process but the process disclosed in the Wagner patent U. S. 1,862,914 has been found particularly well suited for surface treating the grains with a liquid explosive nitric ester. Ordinarily, double base smokeless powder grains will contain from 5 to 30% nitroglycerin or other liquid explosive nitric ester and each of the deterrents of this class is more effective than its normal counterpart on such grains. They may also be used to advantage in smokeless powder grains containing even more or less liquid explosive nitric ester.

As pointed out hereinbefore, the deterrent may be applied to the surface of the grains by any suitable method. In one method about parts smokeless powder grains may be suspended inan emulsion of about 9 parts of the diisoalkylphthalate deterrent such as diisobutylphthalate, about 0.75 part by weight emulsifying agent such as gum arabic and about 500 parts water. The grains are agitated in this slurry for about five hours after which they are separated from the liquid phase and air dried. The grains resulting from such treatment will have a surface coating of about 8% diisobutylphthalate.

As an example of one advantage derived from the use of one of the diisodialkylphthalates as a deterrent, spherical grains of gela'tinized nitrocellulose base were formed in accordance with the method disclosed by Schaefer in U. S. 2,160,626 and thereafter coated with about 15% nitroglycerin as disclosed in U. S. 1,862,914 were coated with about 4% diisobutylphthalate in accordance with the emulsion coating process described in the foregoing. Substantially identical smokeless powder grains were coated in the same manner with an equal amount of normal dibutylphthalate. These grains were stored three months at 140 F. and then suitable charges thereof were loaded in caliber .308 Winchester cartridges with a grain bullet and fired. It was found that the pressure developed in the breech of the gun when cartridges containing the powder having the diisobutylphthalate coating were fired was only about 1200 pounds per square inch higher than the 50,400 pounds per square inch pressure developed in the breech of the gun 3 months earlier with the same lot of powder immediately after it had been made. Cartridges containing the normal dibutylphthalate however, developed a pressure of 11,000 pounds per square inch more than the original pressure of 52,000 pounds per square inch developed by the same lot of powder three months earlier immediately after it had been made. These results indicate that the diisobutylphthalate retained its effectiveness after extended storage at elevated temperatures whereas the normal dibutylphthalate was much less effective.

A laboratory test has been devised to determine the relative merits of various deterrents insofar as ballistic stability after extended storage periods is concerned. This method is based on the migration rate of the deterrents in nitrocellulose bodies. In comparing the diisoalkylphthalates with the dialkylphthalates, films of nitrocellulose about 2 mils thick were cast and one film was stretched between two clamps and suspended in a liquid bath of each of the deterrents. One of the clamps was provided with a Weight in order to stretch the film tightly. The length of time required for the film to break apart under the weight was measured and the following results were obtained:

Cast film migration results The abbreviations in the foregoing table were used for the following deterrents:

D PrPNrmal dipropylphthalate D IPrPdiisopropylphthal ate D B PN0rmal dibutylphth alate DI B Pdiisobutylphthalate D A P Normal diarnylphthalate D IA P-diisoamylphthalate These results indicate that each of the diisoalkylphthalates is advantageous over its normal dialkylphthalate counterpart in double base powders because the time required for breakage of the film is directly dependent upon the rate of migration of the deterrent into the film. These results have been found to truly indicate the relative stability of smokeless powder grains having one of the various deterrent coatings thereon because as the rate of migration of the deterrent inwardly increases the instability of the powder grains decreases.

The solvent and plasticizer properties of the class of deterrents provided by this invention have been found to be conducive to rapid adsorption at the surface of the smokeless powder grain and into the grains interior to the extent required to provide proper ballistic characteristics during the coating process, yet no appreciable migration occurs after coating even at elevated temperatures. The resulting powder grains are substantially free from tack and no trouble has been encountered from the grains becoming agglomerated. The deterrents may be dissolved in a solvent therefor which is a non-solvent for the smokeless powder base and can be applied from this solution to the surface of the grains. Such solvents include benzene, toluene, chlorinated hydrocarbons and the like.

The invention has been described in considerable detail in the foregoing but it is to be understood that many variations may be made by those skilled in the art without departing from the scope of the invention except insofar as it is limited by the appended claims.

I claim:

1. Smokeless powder grains having a nitrocellulosenitroglycerin base, the outer one-sixth of the grains being impregnated with from about 2 to about 15 percent of a diisoalkylphthalate having from 3 to 6 carbon atoms in the alkyl chain.

2. Nitrocellulose-nitroglycerin smokeless powder grains having a coating of a diisoalkylphthalate having from 3 to 6 carbon atoms in the alkyl chain the coating being between about 2 percent and about 15 percent of the weight of the grains.

3. Smokeless powder grains having a nitrocellulosenitroglycerin base and surface treated with from about 2 percent to about 15 percent diisopropylphthalate.

4. Smokeless powders grains having a nitrocellulose nitroglycerin base and surface treated with from about 2 percent to about 15 percent diisobutylphthalate.

5. Smokeless powder grains having a nitrocellulosenitroglycerin base and surface treated with from about 2 percent to about 15 percent diisoamylphthalate.

6. Smokeless powder grains having a nitrocellulosenitroglycerin base and surface treated with from about 2 percent to about 15 percent diisohexylphthalate.

7. Smokeless powder grains having a nitrocellulosenitroglycerin base, the outer one-sixth of the grains be ing impregnated with a diisoalkylphthalate having from 3 to 6 carbon atoms in the alkyl chain and substantially devoid of any deterrent in the remainder of the grain.

References Cited in the file of this patent UNITED STATES PATENTS 

7. SMOKELESS POWDER GRAINS HAVING A NITROCELLULOSENITROGLYCERIN BASE, THE OUTER ONE-SIXTH OF THE GRAINS BEING IMPREGNATED WITH A DIISOALKYLPHTHALATE HAVING FROM 3 TO 6 CARBON ATOMS IN THE ALKYL CHAIN AND SUBSTANTIALLY DEVOID OF ANY DETERRENT IN THE REMAINDER OF THE GRAIN. 